Generally nylon is toughened by rubber, such as ethylene-propylene rubber, terco-ethylene-propylene rubber, butadiene-acrylonitrile rubber, butadiene-styrene rubber, or thermoplastic elastomer, such as styrene-butadiene-styrene copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), ethylene-vinyl acetate copolymer (EVA) and ethylene acrylic acid copolymer (EAA). However as the compatibility of these components with matrix nylon is very poor, a solubilizer must be added, such as elastomers grafted with maleic anhydride (for example, polyethylene-g-maleic anhydride (E-g-MAH), thermoplastic elastomer-g-maleic anhydride (TPE-g-MAH) and others). The nylon prepared by the above process is an alloy-polymer in morphology and the preparation process is rather complicate.
Casting nylon has high molecular weight and excellent mechanical performance. However as large-size article formed by casting process often tends to break due to poor toughness and also has high notch sensitivity, modification is necessary. In prior art the toughening method of casting nylon-6 is mainly copolymerization with dodecanolactam or modification with rubber component. Therefore the modifying agents adopted are mainly amino capped polyoxyethylene oxide, polypropylene oxide or their copolymers, amino capped liquid polybutadiene or butadiene-acrylonitrile rubber. For example, in U.S. Pat. Nos. 4,882,382, 4,994,524 and 5,189,098 casting nylon is toughened by core-shell polymer. An aqueous dispersion of polymer consisting of elastomer core and hard thermoplastic shell is prepared, and the aqueous dispersion is mixed with the aqueous solution of hexanolactam to obtain a dispersion after dehydrating. Then such dispersion, catalyst and hexanolactam are polymerized to obtain Nylon-6 toughened by rubber, in which the content of core-shell polymer is generally over 10%. The preparation process of said toughening agent is complicate and difficult in operation.
Nylon prepared by hydrolysis condensation polymerization or screw reacting extrusion is mainly toughened by rubber or reactive toughening agent with low molecular weight. Or resin prepared hereby is toughened by rubber or elastomer in screw extrusion process.
However in all said toughened nylons the rubber or thermoplastic elastomer do not dissolve in the lactam monomer of nylon, so that the rubber or elastomer exists in matrix nylon as a dispersed phase. The property of nylon depends on the extent of dispersed phase, and the crystallinity of nylon and the strength of article formed with said nylon exhibit a great reduction. Therefore it is difficult to toughen casting nylon successfully by rubber or thermoplastic elastomer as toughening agent.